This collaborative project brings together two investigative teams with over two decades of combined research experience in (1) the treatment of reperfusion injuries after global cerebral ischemia due to cardiac arrest and resuscitation, (2) mechanisms of neuronal injury and protection through systemic immune responses, and (3) systemic drug delivery to the central nervous system (CNS). In their search for effective treatment of global cerebral ischemia using adult stem cells, the investigators serendipitously discovered a novel mechanism of stem cell protection through cell signaling instead of transdifferentiation or stem-cell/host-cell fusion. Most importantly, the investigators found that this signaling process can strongly modulate the inflammation response to global ischemia and render protection to selectively vulnerable neurons by preventing pro- inflammatory damage to glial cells. The main objective of this project is to achieve a mechanistic understanding of the coupling between systemic and brain immune responses to global cerebral ischemia, thereby developing a systemic treatment strategy to approach neuronal repair after cardiac arrest. The central hypothesis is that most of the disseminated neuronal loss in the later phase of reperfusion after resuscitation can be prevented and reversed by tailoring the immune system to turn off pro-inflammatory responses and turn on protective immune activation. An innovative approach is proposed to hijack the immune cells' natural repairing potential and to shape their functional secretion of cytokines for a previously uncharted therapeutic territory. A clinically relevant outcome model of cardiac arrest and resuscitation in mice has been developed to allow the use of partially and completely immunodeficient transgenic mice in longitudinal survival studies after a well-controlled cardiac arrest and resuscitation. The specific aims of this project are: Specific Aim 1: To establish correlations between systemic and brain immune responses to global cerebral ischemia and reperfusion injuries after clinically relevant cardiac arrest in immunocomplete wild-type mice; Specific Aim 2: To use partially and completely immunodeficient transgenic mice to identify and differentiate immune contributions from pro- and anti-inflammatory cytokines in neuronal injury and repair; Specific Aim 3: To engineer bone-marrow-derived macrophagic and dendritic cells to restore the targeted immune response in partially and completely immunodeficient mice to achieve a mechanistic understanding of the underlying processes in systemic immune responses in neuronal injury and protection; and Specific Aim 4: To develop possible in vivo post-treatment strategies focusing on rebalancing the pro- and anti-inflammatory cytokines using RNA-interference technology in wild-type mice after cardiac arrest and resuscitation. These specific investigations will pave the way to ultimately identifying the most effective strategies to treat global ischemia after cardiac arrest, and to bridge new mechanistic understandings from benchtop to bedside.